1. Field of the Invention
The present invention relates to a transducer supporting apparatus for a rotary memory, and particularly to a transducer supporting apparatus which is suitable for a high-density memory wherein the transducer floatation amount is small and the search speed thereof is high.
2. Description of Prior Art
A rotary memory is provided with a rotating storage medium, a transducer for reading and writing information in the state of being floated above the storage medium, a transducer supporting apparatus such as the one disclosed, for example, in U.S. Pat. No. 4,167,765, for supporting the transducer, and an access mechanism for giving the transducer access to the storage medium and for supporting it at any desired position within the radius thereof. The transducer supporting apparatus is provided with a flexible structural support comprising a rectangular notch which forms two outer flexible fingers connected by means of a slightly-flexible transverse frame, a flexible central tongue which extends from the transverse frame to the notch, a rigid structural support for supporting the flexible structural support comprising an elastic portion and a load beam portion, and a projection for transmitting load interposed between the rigid structural support and the central tongue of the flexible structural support, the air bearing slider (referred to as "slider" hereinafter) loaded with the transducer being provided on the central tongue.
The transverse frame is formed into a solid form and the central tongue is substantially rigid because the slider is provided on the lower surface thereof and, consequently, the outer flexible fingers are the only substantially flexible portions of the flexible structural support. The outer flexible fingers are formed in parallel with the central tongue and thus in parallel with the plane formed by the floating surfaces of the slider.
During a search in which the transducer is given access to any radial position of the rotary medium, a radial driving force is applied to the transducer supporting apparatus from the access mechanism. This driving force effects acceleration, speed maintenance, or deceleration of the transducer supporting apparatus. In the above-described conventional transducer supporting apparatus, insufficient account has been taken of the phenomenon whereby when the driving force is applied, the slider rolls and thus reduces the floatation amount, as described below.
In other words, since there has been so far no means for precisely measuring any variation in the floatation amount with time at a high speed and, thus, of simultaneously measuring the changes of the floatation amounts of the right and left floating surfaces of the slider and detecting the rolling movement of the slider, it has not been possible to take the above-described phenomenon sufficiently into consideration. Here, "precise measurement" of the change in floatation amount at high speed means that a change in floatation amount of about 0.01 .mu.m produced within a time 0.5 mS can be measured with a resolution of 0.05 mS to 0.1 mS and 0.005 .mu.m or more.
Another reason for the fact that insufficient consideration has been given to reductions in floatation amount during search in the prior art is that the actual floatation amount is normally sufficiently large compared with the amount of any estimated reduction which takes place during the search. Namely, it has been previously thought that an ordinally floatation amount is 0.4 .mu.m to 1 .mu.m, while any reduction in the floatation amount is on the order of 0.01 .mu.m to 0.03 .mu.m and hence not critical factor. However, recent developments have led to the use of increasingly high levels of storage density and it has become necessary to reduce the floatation amount to the range of 0.2 .mu.m to 0.3 .mu.m. There is also nowadays a demand for search time to be reduced. Thus any reduction in the floatation amount during search becomes larger than the conventional amount, and hence it becomes necessary to take sufficient account of this reduction in floatation amount during the search.
A conventional concept with respect to the cause of a reduction in floatation amount during search will be described hereinafter.
When a force F in the search direction is transmitted to the slider from the flexible structural support, this force F has the tendency to rotate the slider around the center of mass G thereof. When the rotation of the slider is considered, it can be assumed that the point of application of the force F lies on the surface on which the slider is mounted. Therefore, if the distance between the force F and the center of mass G (an arm length) is l.sub.1, its moment M.sub.G is EQU M.sub.G =Fl.sub.1 . . . (1)
The moment M.sub.G is in balance with a restoring moment M.sub.r which is produced by inclination of the slider by an angle i brought about by a change .+-..DELTA.h in the floatation amount of the floating surfaces of the slider, and thus EQU M.sub.r =k i . . . (2)
wherein k denotes a restoring air bearing spring constant. Since EQU .DELTA.h=l.sub.2 i . . . (3) EQU F=m.alpha. . . . (4),
the above-described change .DELTA.h can be expressed by the following formula: EQU .DELTA.h=m/k l.sub.2 l.sub.1 . . . (5)
wherein m denotes the mass of the slider, .alpha. denotes the search acceleration and l.sub.2 denotes the distance between the left and the right floating surfaces of the slider.
In order to confirm the correctness of the above-described concept, a means for measuring a change in the floatation amount of the floating surface of the slider with time was developed and changes .DELTA.h relative to various masses m and arm lengths l.sub.1 of the slider were measured during search of the transducer supporting apparatus. As a result, it was found that actually measured changes .DELTA.h were very much larger than the value obtained from the formula (5). That is, when L represents a distance between the substantial point of application of the force F on the slider in the search direction and the center of mass G and .DELTA.h is expressed by the following formula EQU .DELTA.h=m.alpha./k l.sub.2 L . . . (6)
it is found that EQU L&gt;l.sub.1 . . . (7)
This is described below in detail. It is found that any deformation of the outer flexible fingers greatly affects the magnitude of .DELTA.h. The reason is as follows. The center of mass G of the slider lies on the side of the storage medium relative to the outer flexible fingers. Thus, when an inertial force (F=m.alpha.) is applied to the slider by the search acceleration .alpha., the outer flexible fingers are deformed in the direction in which the change .DELTA.h is further increased thereby.
In the conventional transducer supporting apparatus, as described above, insufficient account has been taken of the large distance between the substantial point of application of a force on the slider in the search direction and the center of mass G of the slider and there therefore has been a problem with respect to the large reduction in floatation amount which occurs during the search.